Apparatus for protecting refractory linings



March 1, 1966 B. KOVACH 3,237,865

APPARATUS FOR PROTECTING REFRACTORY LININGS Filed July 50, 1963INVENTOR. 55m flaw: CH

United States Patent Ofiice 3,237,865 Patented Mar. 1, 1966 3,237,865APPARATUS FOR PRQTECTING REFRACTQRY LENINGS Bela Kovach, New York, N.Y.,assignor, by direct and mesne assignments, to Arnlico FurnasprayCorporation, New York, N.Y., a corporation of New York Filed July 30,1963, Ser. No. 298,609 1 Quinn. (Cl. Z39142) In general, this inventionis concerned with an improved method and associated apparatus forspraying a protective coating on the refractory lining of furnaces whilethe furnace is in operation.

The refractory lining of furnaces, such as the open hearth electric andbasic oxygen furnaces used in melting steel, are exposed to severeoperating conditions. With the extensive use of oxygen, highertemperatures are now employed in the process of melting steel and thereare also sudden changes of temperature which require that the refractorylinings Withstand severe thermal shocks. In addition, the linings areattacked by iron oxide fumes as well as the iron and lime deposits whichare thrown up on the lining. As a result of these more severe operatingconditions, the lining deteriorates faster, such deterioration takingthe form of fiuxing, peeling, spalling and burning.

To preserve the lining, it is standard to spray it with arefractory-cement coat. This cement coat is sprayed directly onto thehot face of the walls and roof of the furnace while the furnace is inoperation. Because of the high operating temperatures, the cement, whenit hits the furnace walls, sinters and bonds to the lining, therebybuilding up the lining.

A wide variety of refractory cements are used for this purpose, howevermost cements contain chrome ore or chrome and magnesite ores (chromeoxides and magnesium oxides). These ores are ground to a powder consistency and are mixed with certain additives to assure proper adhesionand bonding to the furnace lining. Sodium silicate is the additivenormally employed for bonding. These oxides plus the sodium silicate aremixed with water to form a slurry which slurry is then sprayed upon thehot face of the furnace wall to build up the protective coat.

In this prior art technique, the ingredients are mixed in a specialmixing unit with water and hot steam for about an hour. The mixing takesas long as one hour in order to insure that the bonding agent, thesodium silicate, is properly dissolved in the water.

In emergency cases, when the molten steel threatens to break through theeroded areas of the lining, very often there was no spray materialimmediately available (due to the required one hour mixing time) and thefurnace had to be taken oif for rebuilding or repair. This constitutedheavy loss in production and expensive repair cost.

In practice, the ingredients (the sodium silicate as well as the ores)are premixed in dry form and shipped to the steel mill in paper bags. Inthe steel mill, this dry mix is in turn mixed with water to form aslurry. Heavy and expensive mixing equipment is required and suchequipment is generally installed in the open-hearth floor far away fromthe furnaces.

After the cement has been mixed with the water in the mixer, theresulting slurry is dumped into a spray gun. The gun is then transportedby crane or forklift truck to the furnaces. Air under pressure is fedinto the spray gun to force the slurry out of the gun, through amaterial hose and into the operating furnace where it is sprayed on theWalls of the furnace to form the desired protective coating.

There are a number of problems which arise in con- Cat nection with thisprior art procedure. The major, but certainly not the only, consequenceof these problems is that a large amount of the slurry fails to adhereto the furnace wall resulting in what is called rebound loss. Thisrebound loss increases the cost of the spray operating and causes somecontamination of the molten metal being processed in the furnace. Anydecrease in, or elimination of rebound loss will result in an improvedprotective coating and efiiciency of spraying.

After the mixed slurry has been dumped into the spray gun, if there isany delay in the actual spraying, the refractory cements will start toharden, to settle and to separate. The critical time period is less than/2 hour. As a consequence, there is lack of uniformity in the mix anduneven flow of the material. At times, the gun will be jammed. Where thehardening has not gone so far as to jam the gun, what occurs is that atthe beginning of the spraying the flow is of dense heavy mix from thebottom of the gun. Near the end of the spraying there is mostly waterfrom the top of the batch. This very weak mix and liquid which issprayed, near the end of such an operation, can do more damage to thehot wall of the furnace than good.

A further separation of refractory cement from liquid occurs in the longhose that leads from the spray gun to the furnace opening. The heavymaterial tends to run at the bottom of the hose while the lighterfraction (liquid and air) tends to run faster on top of the heaviermaterial. The slower running heavier slurry at the bottom of the hose isthus insufiiciently atomized at the hose outlet and consequently doesnot properly sinter and bond to the furnace wall.

As a consequence of the separation within the gun and of the separationin the long hose, as much as 30% to 50% of the cement will be lost inrebound loss. This is not only uneconomic in terms of refractory cementmaterial but also creates a contamination problem for the steel, andparticularly for alloys, being manufactured.

For the sintering and bonding process to operate properly so that therewill be a minimum of rebound loss, it is necessary that the cement oresbe finely mixed throughout the slurry so that each particle isthoroughly exposed to the high heat of the furnace, which exposure isrequired for proper sintering and bonding.

In brief, this invention involves a new approach towards the preparationand application of protective coatings to the refractory lining offurnaces. This new method calls for a preliminary mixing of the bondingmaterial with sufficient water so as to dissolve the bonding material.This premixed bonding agent can then be readily mixed with theprotective coating powders. Because the mixing may be more readily done(5-10 minutes as contrasted with 1 hour) it becomes possible to have themixing occur in the gun which is used to spray the protective coating onthe furnace walls. Accordingly, this invention also provides an improvedgun which includes an agitator so that the final material may be mixedin the gun before spraying. The agitator has the further advantage thatit prevents the protective powders from settling out of the mixedmaterial during the time it takes to use up a single charge for the gun.In this fashion, the combination of a partial premixing of binder withwater and the use of an agitator within the pressure gun provides a moreuniform, better mixed spray which flows more evenly and which makes itpossible to greatly increase the efi'iciency of use of the spraymaterials.

This invention further provides a small nozzle pipe mixer attached tothe steel pipe nozzle near the end of the spraying hose so that theadvantages gained [by the partial premixing of bonding material and theuse of an agitator are not partially lost through the settling out ofthe protective material during travel from the gun through somewherebetween and to the vertical.

the spraying hose to the exit nozzle from the spraying hose.

Other objects and purposes of this invention will become apparent from aconsideration of the following drawings and detailed description, inwhich:

FIG. 1 is a partially broken away mechanical schematic of the apparatusinvolved in this invention;

FIG. 2 is a longitudinal cross section of the novel nozzle pipe mixeremployed in this invention; and

FIG. 3 is an isometric view of the mixer of FIG. 2.

FIG. 1 illustrates the container or vessel of a spray gun 11 which inmany respects is similar to the prior art spray gun but which has beenmodified in certain respects for use in this invention. To this gun 11there is connected a main air supply line 12 and a long hose 14 forspraying the inside of the furnace walls with the slurry from which therefractory cement coat is formed.

The gun 11 itself is mounted on a frame 16, which frame 16 is designedso that the gun may be carried by or maintained on a forklift truck.Alternatively, the gun may be transported by means of a crane and chainwhich lifts the spray gun 11 by the eyes 18. The opening 20 that isshown is used to feed a charge of powdered ores and additives togetherwith the specially prepared concentrated sodium silicate liquid. Theopening 20 is simply adapted from the prior art guns where such anopening is a manhole provided for the purpose of cleaning out the spraygun. A standard water feed and overflow 22 is shown, which water feedincludes a water meter, for the purpose of adding a measured amount ofwater to the charge that is added through the opening 20. A plug 23which is shown at the base of the gun 11 is also used for cleaningpurposes.

More important to the particular operation of this invention is theinclusion of a means for mixing the material, the agent and water whilein the spray gun 11. The mixing means illustrated involves twopropellers 24 which are mounted on a shaft 26 in such a fashion thatthey can be adjusted longitudinally along that shaft 26. A motor 28drives the shaft 26 through a speed reducer 29'. To obtain maximumefficiency of mixing, it has been found preferable to maintain thepropeller shaft 26 at an angle Two propellers 24 are shown as it hasbeen found that two propellers provide adequate mixing in the standardsize spray gun 11. In one preferred embodiment each propeller has a tipto tip span of approximately eight inches.

As may be seen in FIG. 1, the agitation provided by the propellers 24and shaft 26 avoids one of the major problems in the prior art. Thatproblem arose out of the settling and separation of the solids in theslurry which settling becomes significant as a problem in about tenminutes after the gun is loaded. Because of the settling, the initialflow from the gun is of a dense heavy mix from the bottom of the gun andthe final flow of slurry is excessively liquid. The excessively liquidslurry frequently does more damage to the hot wall of a furnace thangood. Since the settling and separation of the material starts to takeplace in about ten minutes after the mixing is completed, any delay inthe use of the gun results in some undesirable separation unless theagitation provided by this invention is present.

The hose 14 is made of a flexible material and generally runs to feetlong. At the end of the hose 14 a rigid metal pipe nozzle 31 isattached. This nozzle 31 generally runs between 12 and 16 feet in lengthand is the portion of the equipment that projects into the furnace whichis to be sprayed. Between the nozzle 31 and the hose 14 there is astandard valve 32. There is added by this invention a mixer pipeassembly 34 between the valve 32 and the pipe nozzle 31. The purpose ofthis mixer assembly 34 is to mix the slurry after it is passed throughthe rather long hose 14 and thus after the solids have had a chance topartially separate out. The mixer assembly 34 is illustrated in greaterdetail in FIGS. 2 and 3 and described below in connection with those twofigures. The major point to be made here is that such a mixer assembly34 is one of the improvements added by this invention to assure that theslurry which is sprayed from the pipe nozzle has an appropriate uniformatomized consistency in which the particles of ore or cement are carriedin fine suspension so that they will properly bond to the furnace wallon which they are sprayed. v

The spray gun 11 end of the flexible hose 14 is con nected to adischarge pipe 36 which extends to near the bottom of the gun 11. Whenthe slurry has been properly mixed in the gun 11 and the air valves 38and 39 are opened, compressed air with a pressure of approximately topsi. is fed into the top of the gun 11 and forces the mixed slurry upthrough the discharge pipe 36 and into the material hose 14. Anadditional opening at the T-shaped elbow 42 permits a portion of thecompressed jet air to be directly fed into the hose 14, when the jet airvalve 40 is turned on, so as to enhance the flow of slurry down the hose14 and pipe nozzle 31.

As the slurry passes down the long hose 14 there is a tendency for thesolids to settle out to the bottom of the hose and for the air and waterto run ahead faster on top of the denser material that is settled down.As a consequence of this settling, the material that is sprayed from thepipe nozzle is inadequately atomized. This invention adds a nozzle pipemixer assembly 34. As may be seen in FIG. 2, the nozzle mixer assembly34 constitutes a sleeve 44 in which there is contained a diverging cone45, a mixer unit 46 and a converging cone 47. The sleeve 44 is screwedonto a connector 48 so that the interior units 45, 46 and 47 are heldtightly within the sleeve 44.

The connector 48, in turn, is screwed onto a pipe nipple 49 on which thevalve 32 operates and which leads to the flexible hose 14. The outletportion of the sleeve 44 is screwed onto the pipe nozzle 31 as shown inFIG. 2. Thus slurry under high pressure is fed through the divergingcone 45 into the mixer 46 where the stationary blades 5i cause theslurry to swirl around sufficiently to provide an even mix. The slurrythen proceeds through the converging cone 47 into the pipe nozzle 31 andthen into the furnace where it is sprayed onto the furnace walls in aproperly atomized and properly distributed form.

The mixer unit 46 has a number of curved blades 50 which are mounted ona hub 51 (see also FIG. 3). The hub 51 and blades 50 cause the effectivecross sectional area of the mixer unit 46 to be less than the requiredcross sectional area of the spray pipe and thus the inner diameter ofthe mixer unit 46 is made sufficiently larger than the diameter of thehose 14 or pipe nozzle 31 so that the effective open cross sectionalarea of the mixer 46 is equal to the cross sectional area of the hose 14(and of the pipe nozzle 31). Accordingly, the diverging cone 45 andconverging cone 47 are provided so that there will be a controlled andrelatively even flow of slurry through the mixer assembly 34 in spite ofthe restrictions.

With reference to the spray gun 11 and associated items described above,the spraying method of this invention can be described as follows. Allthe solids, except the sodium silicate, that are required for theappropriate slurry are mixed together in powder form. The importantoperative solids are chrome oxides and magnesium oxides which aregenerally referred to as chrome ore and magnesite ore and are broadlyreferred to as the cement ores. In this fashion a dry powder is obtainedwhich can be packaged as such for direct loading into the gun 11.

In addition there is separately packaged a mixture of sodium silicatewith just enough water so as to dissolve the sodium silicate. The amountof water used to dissolve the desired quantity of sodium silicate is tosome extent a matter of choice but economy in shipment costs dictatesthat as little water as possible be used and the purpose of thisinvention which is to provide a ready mix in the spray gun 11 dictatesthat as much water as is necessary to dissolve the sodium silicate isused.

The sodium silicate that is thoroughly pre-mixed with a minimum amountof water necessary to dissolve it forms a sodium silicate liquidconcentrate which can be shipped in plastic containers to the furnacesite, along with the dry cement in separate paper bags, from whateverplant or source manufactured the furnace coating material.

This dissolved sodium silicate is then also loaded into the gun 11through the opening 20. The rest of the water needed to make theappropriate slurry is then added through the water feed 22 or chargeopening 20, while the motor 28 is turned on to assure a proper mixing ofthe water, dissolved sodium silicate and dry powder cement mix.

In preparing the slurry in the spray gun 11, the sodium silicate liquidconcentrate is added to the total amount of additional water requiredfor the spray mix. The additional amount of water required isapproximately three to four times as much as is present in theconcentrate. After the sodium silicate concentrate has been properlydiluted, the dry cement mix is added to the solution and agitated forapproximately five to ten minutes, after which time the slurry is readyfor spraying.

There is accordingly a considerable time saving over the one hour mixingtime required by the prior art method, which prior art method involvedhaving to mix and dissolve the sodium silicate and the refractorycements in dry form, on the job site. In addition, since it becomespossible to mix the materials inside the gun 11, it becomes possible toeliminate the need for the heavy and expensive mixing machinery that washitherto required and the necessity of using hot steam for thedissolving of sodium silicate. Economy of time and in the use ofequipment thus become major advantages of the method taught by thisinvention.

One advantage obtained by the teachings of this invention is that thespray gun 11 does not have to be transported between the mixingequipment and the furnace for loading and for use. Thus the cranes whichare frequently used for transporting the spray gun need not be divertedfrom their normal use in loading the furnace. In this fashion, there isan additional facet to the speeding up of the operation of the steelmill.

What is claimed is:

A spray gun assembly for spraying a slurry of refractory cement on theinner walls of an operating refractory furnace, said assembly comprisingin combination with:

a spray gun container, having an opening for receiving a charge,

a main air supply line connected with said container,

a water and overflow feed connected with said container,

a plug closing an opening at the base of said container,

a shaft extending through another opening at the top of said containersubstantially close to the bottom thereof, said shaft extending at anangle of substantially 30 to 35 to the vertical,

two propellers mount-ed upon said shaft and rotatable therewith, saidpropellers being longitudinally adjustable upon said shaft,

a valve member located outside of said container,

means opening and closing said valve member,

a pipe connecting said air supply line with said valve member,

a valve carried by said pipe,

at discharge pipe connected to said valve member and extending through afurther opening at the top of said container substantially, close to thebottom thereof,

a hose having one end connected to said valve member,

and

an elongated pipe nozzle,

a mixer assembly comprising a sleeve,

means connecting one end of said sleeve with said hose, said pipe nozzlebeing connected with the other end of said sleeve,

a diverging cone located within said sleeve adjacent the last-mentionedmeans,

a converging cone located within said sleeve adjacent said pipe nozzle,

and a mixer unit located within said sleeve between said cones andconsisting of a plurality of curved blades, and

a hub carrying said blades.

References Cited by the Examiner UNITED STATES PATENTS 593,732 11/1897Burck 239142 2,075,867 4/1937 Sampel 259151 2,348,395 5/ 1944 Larson264-30 2,419,410 4/ 1947 Maurer 259-151 2,435,605 2/ 1948 Rowell 2394882,809,126 10/ 1957 Murphy 26430 2,959,358 11/1960 Vork 239-142 3,025,0063/1962 Maurath 239142 FOREIGN PATENTS 735,384 8/1932 France.

EVERETT W. KIRBY, Primary Examiner.

ALEXANDER H. BRODMERKEL, Examiner.

